ANTIOXIDANT ENZYME AND COMPOUND RESPONSES TO CHILLING STRESS AND THEIR COMBINING ABILITIES IN DIFFERENTIALLY SENSITIVE MAIZE HYBRIDS

Chilling sensitive species often have lower antioxidant capacities tha n do tolerant species. This study was conducted to determine if antiox idant capacities and carbohydrate concentrations would be useful in a proposed screening technique for chilling sensitivity in maize (Zea ma ys L.). Leaves of 12 maize hybrids exhibiting differential sensitivity to chilling were harvested at the third-leaf stage under either (i) a constant 25 degrees C control regime or (ii) the control regime plus a short-term chilling shock of 11 degrees C for 1 d prior to harvestin g. Catalase (CAT; EC 1.11.1.6), monodehydroascorbate reductase (MDHAR; EC 1.6.5.4), and ascorbate peroxidase (ASPX; EC 1.11.1.11) activities were assessed. Carbohydrate levels were determined as general metabol ic indicators of chilling stress. The chill/control ratios of CAT, MDH AR, and ASPX were lowest and concentrations of carbohydrates highest i n the most chilling sensitive hybrids. Differences between hybrids in antioxidant capacities to detoxify toxic oxygen compounds may be impor tant in differential chilling sensitivity. The higher chill/control ra tios of carbohydrates in the sensitive hybrids after chilling indicate d that their rate of assimilate utilization was reduced by the chillin g treatment more so than those of the chilling tolerant hybrids. Activ ities of CAT, MDHAR, and ASPX and concentrations of carbohydrates woul d thus make excellent indicators of chilling stress in a screening tec hnique for chilling sensitivity of maize.